Add ChangeloG verifier workflow

Signed-off-by: Owais <owaiskazi19@gmail.com>

Author: owaiskazi19

.github/workflows/changelog_verifier.yml

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+name: "Changelog Verifier"
+on:
+  push:
+    branches-ignore:
+      - 'whitesource-remediate/**'
+      - 'backport/**'
+  pull_request:
+    types: [opened, edited, review_requested, synchronize, reopened, ready_for_review, labeled, unlabeled]
+
+jobs:
+  # Enforces the update of a changelog file on every pull request
+  verify-changelog:
+    if: github.repository == 'opensearch-project/anomaly-detection'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      - uses: dangoslen/changelog-enforcer@v3
+        with:
+          skipLabels: "autocut, skip-changelog"

CHANGELOG.md

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+# CHANGELOG
+All notable changes to this project are documented in this file.
+
+Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
+
+## [Unreleased 3.0](https://github.com/opensearch-project/anomaly-detection/compare/2.x...HEAD)
+### Features
+### Enhancements
+### Bug Fixes
+### Infrastructure
+
+### Documentation
+
+### Maintenance
+### Refactoring
+
+## [Unreleased 2.x](https://github.com/opensearch-project/anomaly-detection/compare/2.19...2.x)
+### Features
+
+
+### Enhancements
+### Bug Fixes
+
+### Infrastructure
+### Documentation
+### Maintenance
+### Refactoring